Welcome to pin:out
The comprehensive GPIO pinout website for the BBC micro:bit
The comprehensive GPIO pinout website for the BBC micro:bit
P10 is wired to Column 3 of the onboard 5x5 pixel LED matrix on the BBC micro:bit.
While the LED matrix is 5x5 (25) pixels, there are 9 columns and 3 rows. Columns 8 and 9 drive only two LEDs each.
While you may use this pin for other purposes, you must take into account that it is wired to LEDs and their associated resistors.